Frequency acquisition for serdes receivers

ABSTRACT

The present invention is directed to data communication. More specifically, embodiments of the present invention provide a method for acquiring sampling frequency by sweeping through a predetermined frequency range, performing data sampling at different frequencies within the predetermined frequency range, and determining a target frequency for sampling data based on a maximum early peak frequency and a maximum late peak frequency. There are other embodiments as well.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 14/696,326 filed Apr. 24, 2015, commonly assignedand incorporated by reference herein for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

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REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

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BACKGROUND OF THE INVENTION

The present invention is directed to data communication.

Over the last few decades, the use of communication networks exploded.In the early days of the Internet, popular applications were limited toemails, bulletin board, and mostly informational and text-based web pagesurfing, and the amount of data transferred was usually relativelysmall. Today, Internet and mobile applications demand a huge amount ofbandwidth for transferring photo, video, music, and other multimediafiles. For example, a social network like Facebook processes more than500TB of data daily. With such high demands on data and data transfer,existing data communication systems need to be improved to address theseneeds. For high-data communication applications, serializer/deserializer(SERDES) is commonly used.

Over the past, there have been many types of communication systems andmethods. Unfortunately, they have been inadequate for variousapplications. More specifically, the SERDES receivers are ofteninadequate. Therefore, improved systems and methods are desired.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to data communication. Morespecifically, embodiments of the present invention provide a method foracquiring sampling frequency by sweeping through a predeterminedfrequency range, performing data sampling at different frequencieswithin the predetermined frequency range, and determining a targetfrequency for sampling data based on a maximum early peak frequency anda maximum late peak frequency. There are other embodiments as well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating a conventional SERDESreceiver.

FIG. 2 is a simplified diagram illustrating a SERDES receiver 200according to an embodiment of the present invention.

FIG. 3 is a graph illustrating a process for determining a samplingfrequency according to an embodiment of the present invention.

FIG. 4 is simplified flow diagram illustrating a process for acquiringsampling frequency according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to data communication. Morespecifically, embodiments of the present invention provide a method foracquiring sampling frequency by sweeping through a predeterminedfrequency range, performing data sampling at different frequencieswithin the predetermined frequency range, and determining a targetfrequency for sampling data based on a maximum early peak frequency anda maximum late peak frequency. There are other embodiments as well.

Providing clock signals is a vital aspect in design and implementationof data communication systems. For example, a typicalserializer/deserializer (SERDES) receiver uses an external clock as areference to generate the recovered clock signal that is used to sampledata. The external clock needs to be of high quality, and frequency ismatched to within a few hundred parts per million of a knownsub-multiple of the data rate. For example, it is common for 28 Gb/sSERDES to require a reference clock of 350 Mhz±0.02%, which isassociated with an 1/80 of the data rate. Such implementation requires acrystal oscillator in the system and associated distribution circuits.

FIG. 1 is a simplified diagram illustrating a conventional SERDESreceiver. As shown in FIG. 1, a reference clock provides a 350 Mhzreference frequency, which is multiplied by a phase-lock loop (PLL) toproduce a clock at the required data rate (or a sub-multiple thereof fora time interleaved system). The clock signal is adjusted, in phase andfrequency, by a phase interpolator to produce clock signals aligned tothe center and edges of the incoming data. An early/late detection logicdetermines whether the clocks are sampling in the center of the eye, andadjusts the controls of the phase interpolator to get the requiredalignment. The external reference clock and the PLL can consume arelatively large amount of power for the SERDES receiver.

SERDES implementations with external clock signals (e.g., SERDESreceiver shown in FIG. 1) can be expensive, both in power and circuitarea. For example, if a SERDES could be implemented without a referenceclock, it could save power in creating and distributing this reference.While it is possible and convenient to generate reference clock signalsusing an on-chip oscillator, it is hard to get the required accuracy inthe face of process, voltage, and/or temperature variations. It is to beappreciated that according to various embodiments of the presentinvention, an on-chip oscillator is configured to provide referenceclock signals, and it is tuned at chip start-up.

The following description is presented to enable one of ordinary skillin the art to make and use the invention and to incorporate it in thecontext of particular applications. Various modifications, as well as avariety of uses in different applications will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to a wide range of embodiments. Thus, the present inventionis not intended to be limited to the embodiments presented, but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

In the following detailed description, numerous specific details are setforth in order to provide a more thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without necessarily being limitedto these specific details. In other instances, well-known structures anddevices are shown in block diagram form, rather than in detail, in orderto avoid obscuring the present invention.

The reader's attention is directed to all papers and documents which arefiled concurrently with this specification and which are open to publicinspection with this specification, and the contents of all such papersand documents are incorporated herein by reference. All the featuresdisclosed in this specification, (including any accompanying claims,abstract, and drawings) may be replaced by alternative features servingthe same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

Furthermore, any element in a claim that does not explicitly state“means for” performing a specified function, or “step for” performing aspecific function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, the use of “step of” or “act of” in the Claims herein is notintended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

Please note, if used, the labels left, right, front, back, top, bottom,forward, reverse, clockwise and counter clockwise have been used forconvenience purposes only and are not intended to imply any particularfixed direction. Instead, they are used to reflect relative locationsand/or directions between various portions of an object.

According to various embodiments, the present invention provides aSERDES receiver that does not rely on external reference clock, PLL, andphase interpolator to process data at correct data rate. By eliminatingthese components from SERDES receivers, large device area and a greatamount of power consumption are saved. An on-chip oscillator has a(digital) input that controls the frequency and an analog input thatadjusts (e.g., advances or retards) the phase of the clocks. The SERDESreceiver additionally includes data samplers, early/late detectionlogic, and accumulator. For example, the data samplers typically includeboth edge clock sampler and data sampler. It is to be appreciated thatSERDES receivers according to embodiments of the present invention canprovide same or greater level of performance as conventional devices,but with lower power consumption and smaller device area.

As explain above, an important aspect of data sampling is to determinethe correct sampling frequencies. In various embodiments, a SERDESreceiver according to embodiments of the present invention sweepsthrough a range of frequencies to determine the digital code to set thesampling frequency. During the frequency sweep process, early/latedetection logic is used to determine the correct frequency. Depending onthe implementation, existing early/late detection logic may beincorporated into the embodiments of the present invention. For example,early/late detection logic may be implemented using phase comparatorssimilar to those used in CDR devices. Using early/late detection logic,the need for high-speed circuitry can be avoided.

As the SERDES receiver sweeps through a range of frequencies, theoscillator generates different frequencies (e.g., from low to high, orhigh to low). The data samplers sample data at these differentfrequencies. If the oscillator is operating at the correct frequencyrange, then the early/late logic will produce approximately equalnumbers of early and late votes, which is counted by the accumulator.More specifically, if the frequency sweeps from low to high, theaccumulator will count a high number of “early” due to frequency beingslightly low, and then as frequency increases (as a part of the sweep)and moves past the correct sampling frequency, the accumulator willcount a high number of “late” due to frequency being slight high. On theother hand, if the oscillator frequency is off by more than the trackingrange of the clock data recover (CDR) loop, which is typically only afraction of a percent, the CDR loop loses lock and the early/latedeterminations are essentially random.

When the sample frequency is far off (i.e., far enough from the actualsampling frequency range), the system is unable to actually acquireactual data at “wrong” frequencies, and wrongly sampled data are mostlynoise. When early/late detection module processes a large number ofwrongly sample data that are mostly noise, the number of “early”determinations is likely to be statically equal to the number of “late”determinations. The accumulator that aggregates the result of theearly/late detection (e.g., each early detection is a “+1” and each latedetection is a “−1”), the sum of early and late over a large sample sizestays at approximately “0” since the number of early detectionsessentially cancel out the number of late detections. On the other hand,if the sample frequency is not too far off, the system is able to bothsample and have meaningful detection as whether the sampling process is“early” or “late”. More specifically, if the sampling frequency is closeenough for the system to sample data but is slightly lower than actualdata rate frequency, the early/late detection module would generate alarge number of “early” detections, and the sum aggregated by theaccumulator will be a positive number that is statistically larger thanthe number of early detections when the sampling frequency is far off.On the other hand, if the sampling frequency is close enough for thesystem to sample data but is slightly higher than actual data ratefrequency, the early/late detection module generates a large number of“late” detections, and the sum aggregated by the accumulator will be anegative number that is statistically much lower than the number ofearly detections when the sampling frequency is far off. By sweeping thefrequency in small steps across a wide range and at each point countingthe early and late votes in a large enough window to have astatistically significant number of samples, a system according toembodiments of the present invention can find the point at the upper andlower ends of the CDR's tracking range. By assuming symmetry, thecorrect point is approximately at the mid-way between these upper andlower frequencies.

FIG. 2 is a simplified diagram illustrating a SERDES receiver 200according to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The SERDES receiver 200includes data sampler 204, which is configured to sample the incomingdata 202 at a sample rate that is based on the clock frequency of thevoltage controlled oscillator (VCO) 206. The data sampler 204 outputssampled data to a deserializer 203. In various embodiments, incomingdata is received through a data communication interface. For example,the data communication interface may be implemented to receive datareceived from one or more optical communication links. The incoming datais characterized by a data rate that is typically unchanged once thereceiver 200 starts operating. The receiver 200 thus needs to determinethe data rate to be used by the data sampler 204 to sample the incomingdata. It is to be understood that the data sampler 204 often use morethan one clocks to perform data sampling. In various embodiments, thedata sampler 204 includes an edge clock sampler and a data clocksampler. The data sampler 204 may include additional samplers as needed.

The data sampler 204 is connected to the detection module 205. Thedetection module 205 determines whether the sample data are early orlate. For example, the detection module 205 can be implemented invarious ways. For example, the detection module 205 may be implementedusing a CDR phase comparator. The detection module 205 may beimplemented in other ways as well. In certain embodiments, the detectionmodule 205 output a number for each of the early/late determinationmade. For example, for each data sample that is determined to be early,the detection module 205 outputs a “+1”, and for each data sample thatis determined to be late, the detection module 205 outputs a “−1”. Theoutput of the detection module 205 is processed by the accumulator 207.For example, the accumulator 207 stores a sum value based on the outputprovided by the detection module 205. For example, if the sum stored andupdated by the accumulator 207 is a large positive number, it means thatthere are many “early” samples determined by the detection module 205,and it is likely that the sampler 204 is sampling and operating at afrequency lower than the data rate of the incoming data. On the otherhand, if the sum stored and updated by the accumulator 207 is a largenegative number, it means that there are many “late” samples determinedby the detection module 205, and it is likely that the sampler 204 isoperating at a frequency higher than the data rate of the incoming data.Among other things, the receiver 200 can use the information stored bythe accumulator 207 to check whether the sampling frequency is correctand to make corrections as needed.

The sampling rate of the data sampler 204, as explained above, isregulated by the clock signal provided the VCO 206. In variousembodiments, the VCO 206 is implemented on the same chip as othercomponents of the receiver 200. For example, the receiver 200 integratescomponents such as communication interface, sampler, detection module,accumulator, VCO, and/or other components on a single chip, whichtranslates to reduced power consumption and chip size when compared toconventional devices. By eliminating the need for external referenceclock module and PLL used in convention SERDES receivers (e.g., receiverillustrated in FIG. 1), system power consumption is greatly reduced.

The VCO 206 is connected to the digital control module 201 and theanalog control module 208. The digital control module 201 providesdigital control for adjusting the frequency of the VCO 206. The analogcontrol module 208 is configured to provide an input that advances orretards the phase of clock signals generated by the VCO 206. Forexample, the digital control module 201 and analog control module 208are implemented as a part of a feedback control loop that adjusts theoutputs of the VCO 206 based on the output of the accumulator 207. Asdescribed above, in a scheme where the accumulator 207 maintains a sumthat is increases by “early” determinations and decreased by “late”determinations, the VCO 206 is configured to increase its outputfrequency when the sum is positive and decrease its output frequencywhen the sum is negative. In various embodiments, the digital controlmodule 201 receives the output of the accumulator and generates controlsignals that changes the frequency output of the VCO 206. The controlsignals from the digital control module 201 may indicate both thedirection and amount of frequency change. For example, a large positivesum from the accumulator 207 means that the digital control module 201causes the VCO 206 to increase the output frequency by a large amount,and a large negative sum from the accumulator 207 means that the digitalcontrol module causes the VCO 206 to decrease the output frequency by alarge amount.

In various implementations, adjustment of clock signal frequencygenerated by the VCO 206 is an on-going process, where the receiver 200monitors the frequency changes using the detection module 205 and theaccumulator 207, and uses digital control module 201 and analog controlmodule 208 to cause VCO 206 to change its output accordingly. It is tobe appreciated that in addition to adjusting sampling frequency whenoperating, the receiver 200 is also configured to determine the samplingfrequency during an initialization process.

FIG. 3 is a graph illustrating a process for determining a samplingfrequency according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, determinationprocess is performed by the receiver 200 illustrated in FIG. 2. In FIG.3, the horizontal axis is for the sampling frequency code, and thevertical axis is for the accumulator output. For example, frequency coderefers to digital code used by the digital control module to control theVCO 206. For example, a “1” in frequency code corresponds to 50 MHz(e.g., a frequency code of 600 represent a frequency of 3 GHz).

To provide an example, the correct sampling frequency code is 730, whichthe receiver does not initially know. So the receivers sweep through afrequency code range from 600 to 800, as shown in FIG. 3. It is to beappreciated that depending on specific application and the operatingcondition thereof, the sweep frequency range may vary, and the frequencyrange is specifically selected to cover the target frequency. Forexample, through the digital control module, the receiver causes the VCOto generate clock signals based control signals from the control modulecorresponding to a frequency code of 600 for a predetermined interval,then a higher frequency (e.g., frequency code 601) for anotherpredetermined interval, and then another, until the frequency code is at800. During each of these intervals, a set number (e.g., 500 samples) ofdata samples are processed by detection module to determine whether eachsample is early or late, and the accumulator module updates a sum valueaccording. The number of samples at each of these intervals is typicallygreater than 500 to ensure that the sample size is statistically largeenough for the frequency acquisition process. It is to be appreciatedthat sweep frequency range, increment step size (e.g., increasingfrequency code by “1” for each step, which may correspond to a 50 MHzchange in frequency) of the frequency sweep, the predetermined intervalfor each of the frequency increment, the number of samples per eachpredetermine interval, and/or other parameters of frequency sweepprocess may be adjusted for the specific implementations.

As the receiver performs frequency sweep, the accumulator moduleprovides an output value (or sum value) during each of the interval, asshown in FIG. 3. For example, the output value is based on the sum ofearly/late detections during a predetermined interval. For example, an“early” detection increases the sum by “1” and a “late” detectiondecreases the sum by “1”. When the frequency is far off from the targetfrequency (e.g., a few percent off), the output value of the accumulatoris mostly noise. For example, as shown in FIG. 3, when the frequency isbetween 600 and 700 in frequency code, the accumulator output oscillatesbetween “+100” and “−100” and mostly stays around “0”. Similarly, whenthe frequency is between 760 and 800 in frequency code, the accumulatoroutput also oscillates between “+100” and “−100”. This is because whenthe sampling frequency is far off, the early and late determinations aremostly randomly noise, and the sums stored by the accumulator oscillatesand centers on zero. For example, if early/late detection is performedon a statistically much larger number (e.g., over 10,000 samples) ofsamples, the sum stored by the accumulator should be very close to zero,as the number of early detections and the number of late detections arelikely to be very close.

On the other hand, once the sweeping frequency is close to the targetfrequency, the sum stored at the accumulator becomes large, and reachesa positive peak at point 301, where there is a maximum number of earlydetections. As the sweeping frequency increases to a lower bondfrequency that is close enough for the sampler to obtain actual datasamples that are mostly “early”, there are many more “early” detectionsthan “late” detections (e.g., late detections most likely come from baddata samples). As sweeping frequency further increases, the samplingfrequency eventually reaches the target frequency code of 730, at point303. At point 303, the accumulator has a sum of about “0”, the samplingfrequency is now correct and there is essentially no early or latedetections. As the sweeping frequency increases further, the number of“late” detection increases, since the frequency is now higher than thetarget frequency. A negative peak is reached at point 302, where thereare a maximum number of late detections. That is, at point 302, thesampling frequency is still capable of sampling data that are “late”,and there are many more “late” detections than early detections that areattributed to bad data samples. As the sweeping frequency increases pastthe frequency at point 302, the number of “late” detection decreases, asthe number of bad data samples increases when the frequency movesfurther away from the target frequency. When the sweep frequency code isat 790, the accumulator sum is again oscillating between “+100” and“−100” and centered around “0”.

To determine the target frequency, the receiver determines a midpointbetween the positive peak 301 (i.e., maximum number of “early”detections) and the negative peak 302 (i.e., maximum number of “late”detections). For example, in FIG. 3 the positive peak 301 is atfrequency code 720, and the negative peak 302 is at frequency code 740,and the midpoint is at the frequency code of 730, which is the targetfrequency stated earlier. In various embodiments, the target frequencyis calculated by a digital control module. For example, the digitalcontrol module stores frequencies associated with the maximum positivepeak and the maximum negative peak, and the digital control modulecalculates the target frequency by averaging these two frequencies. Forexample, average of frequency code 730 is calculated from the maximumpositive peak frequency code 720 and the maximum negative peak frequencycode 730.

In various embodiments, the frequency acquisition process describedabove is performed at the start of receiver operation on each link whenthe receiver starts receiving data at a specific data rate frequency.Once the target frequency is acquired, the frequency acquisition processis stopped and it does not need to be performed again unless the datarate or frequency changes.

FIG. 4 is simplified flow diagram illustrating a process for acquiringsampling frequency according to an embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. For example, one ormore steps may be added, removed, repeated, rearranged, modified,replaced, and/or overlapped, which should not unduly limit the scope ofthe claims.

At step 401, a frequency acquisition process is initiated. According tovarious implementations, frequency acquisition process is performed whenthe receiver system starts, or when data rate changes, whichnecessitates a change in sampling rate.

At step 402, various frequency acquisition parameters are selected. Forexample, frequency acquisition parameters includes sweeping frequencyrange, step size, number of data samples to be collected at eachfrequency, and/or other parameters. Using these parameters, n samplingprocesses are performed for each of the m frequencies, at step 403.Typically, n is greater than or equal to 500, which represents astatistically significant number of samples with small less likelihoodof statistical anomaly. On the other hand, if n is too large (e.g., over10,000 samples), the sampling time and consequently the startup timemight be too long. Within the sweeping frequency range, m number offrequencies is scanned. For example, for frequency code between 600 and800, a step size of “1” frequency code means m=200. For the frequencyacquisition process, a total of at least m*n samples are processed.

For each of the m*n samples, the detection logic (e.g., early/latedetection logic) determines its sampling position, which could be inposition, early, or late, at step 404. For example, detection logic usesphase calculation to determine the position of the sampled data.

The results of the detection logic are then used by an accumulator tocalculate a sum for each of the frequencies, at step 405. For example,the accumulator adds a “1” to the sum when a sample is determined to beearly, and it adds a “−1” when a sample is determined to be late. Invarious embodiments, the accumulator stores at least m sums, each of thesums corresponding to a sample frequency. As explained above, when thesampling frequency is far off, the results from the detection logic aresubstantially random, and the sum for that frequency is typically smalland hovers around “0”. However, as sample frequency is close enough, alarge number of sampled data are likely to be early or late. The earlyand late peaks are used to determine the target sampling frequency.

At step 406, the maximum early peak frequency is determined. Forexample, the maximum early peak frequency can be determined by comparingall the sums calculated and stored by the accumulator and selecting thegreatest sum. Each of the sums corresponding to the detection result sumof n samples at one of the m frequencies. Since each early detectionincreases the sum by “1”, the maximum early peak frequency can bedetermined by finding frequency corresponding to the largest sum.

At step 407, the maximum late peak frequency is determined. For example,the maximum late peak frequency can be determined by comparing all thesums calculated and stored by the accumulator and selecting the greatestnegative sum. Each of the sums corresponding to the detection result sumof n samples at one of the m frequencies. Since each early detectionchanges the sum by “−1”, the maximum late peak frequency can bedetermined by finding frequency corresponding to the lowest sum.

At step 408, the target frequency is calculated by using the two peakfrequencies determined at steps 406 and 407. As explained above, thetarget frequency is typically at midpoint between the maximum early peakfrequency and the maximum late peak frequency. In a specific embodiment,the target frequency is calculated by averaging the maximum early peakfrequency and the maximum late peak frequency. Depending on theimplementation, the target frequency can be interpolated using the twopeak frequencies in various ways.

The frequency acquisition process does not need to be performed manytimes. Typically, frequency sweep and determination is performed only atsystem start, reset, or data rate change events. At step 409, thefrequency acquisition process terminates. Upon termination of thefrequency acquisition process, the system uses the target frequency fordata sampling. Depending on the implementation, additional frequencyadjustment may be performed as a part of the system operation. There canbe other steps to be performed as well.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. A SERDES apparatus comprising: a receiver devicecomprising: a data communication interface for receiving incoming dataat a first date rate; a data sampler configured to process the incomingdata using an adjustable rate of a clock signal to generate sampleddata; a detection logic configured to determine sampling positions forthe sampled data, the sampling positions including early and latedeterminations; an accumulator for generating an output value based onthe sampling positions, a digital control module configured to generatefrequency control signals based on the output value; and an oscillatorconfigured to generate the clock signal, the adjustable rate beingassociated with the frequency control signals; wherein the receiverdevice is configured to: initiate a frequency acquisition process;perform n sampling processes on the incoming data at m frequencies togenerate n data samples at each of the m frequencies, a total of n*msampling processes being performed, the m frequencies being within apredetermined frequency range, n being associated with a number ofsampling processes, m being associated with a number of frequencies;determine sampling positions for each of the n data samples at each ofthe m frequencies by the detection logic; calculate m sums for the mfrequencies by the accumulator, each of the m sums being calculatedusing sampling positions of n data samples; determine a first peakfrequency, the first peak frequency being associated with a maximumearly detection sum; determine a second peak frequency, the second peakfrequency being associated with a maximum late detection sum; calculatea target sampling frequency using the first peak frequency and thesecond peak frequency; and perform data sampling at the target samplingfrequency using the data sampler; and an interface coupled to the datacommunication interface.
 2. The apparatus of claim 1 further comprisingan analog control module coupled to the oscillator.
 3. The apparatus ofclaim 1 wherein the data sampler is coupled to a deserializer module. 4.The apparatus of claim 1 wherein the oscillator comprises a voltagecontrolled oscillator.
 5. The apparatus of claim 1 wherein the receiverdevice is configured to perform at least m*n sampling processes duringthe frequency acquisition process.
 6. The apparatus of claim 1 furthercomprising an analog control module configured to adjust phases of theclock signal.
 7. The apparatus of claim 1 wherein each of the mfrequencies corresponds to a frequency code.
 8. The apparatus of claim 1wherein the data sampler comprises an edge clock sampler and a dataclock sampler.
 9. A SERDES communication apparatus comprising: anetwork; a data communication link coupled to the network; a datacommunication interface for receiving incoming data via the datacommunication link at a first date rate; a data sampler configured toprocess the incoming data using an adjustable rate of a clock signal togenerate sampled data; a detection logic configured to determinesampling positions for the sampled data, the sampling positionsincluding early and late determinations; an accumulator for generatingan output value based on the sampling positions; a digital controlmodule configured to generate frequency control signals based on theoutput value; an oscillator configured to generate the clock signal, theadjustable rate being associated with the frequency control signals; anda deserializer configured to process the sampled data; wherein theapparatus is configured to: initiate a frequency acquisition process;perform n sampling processes on the incoming data at m frequencies togenerate n data samples at each of the m frequencies, a total of n*msampling processes being performed, the m frequencies being within apredetermined frequency range, n being associated with a number ofsampling processes, m being associated with a number of frequencies;determine sampling positions for each of the n data samples at each ofthe m frequencies by the detection logic; calculate m sums for the mfrequencies by the accumulator, each of the m sums being calculatedusing sampling positions of n data samples; determine a first peakfrequency, the first peak frequency being associated with a maximumearly detection sum; determine a second peak frequency, the second peakfrequency being associated with a maximum late detection sum; calculatea target sampling frequency using the first peak frequency and thesecond peak frequency; and perform data sampling at the target samplingfrequency using the data sampler.
 10. The apparatus of claim 9 whereinthe oscillator and the data sampler are implemented on a semiconductorchip.
 11. A method of operating a SERDES APPARATUS, the methodcomprising: initiating a frequency acquisition process; selecting afrequency range; performing n sampling processes on incoming data at mfrequencies to generate n data samples at each of the m frequencies, them frequencies being within the frequency range, n being associated witha number of sampling processes, m being associated with a number offrequencies, a total of n*m sampling processes being performed;determining sampling positions for each of the n data samples at each ofthe m frequencies by a detection logic data, the sampling positionsincluding early and late determinations; calculating m sums for the mfrequencies by an accumulator, each of the m sums being calculated usingsampling positions of n data samples; determining a first peakfrequency, the first peak frequency being associated with a maximumearly detection sum; determining a second peak frequency, the secondpeak frequency being associated with a maximum late detection sum;calculating a target sampling frequency using the first peak frequencyand the second peak frequency; terminating the frequency acquisitionprocess; and performing data sampling at the target sampling frequencyusing a data sampler; and transferring the incoming data.
 12. The methodof claim 11 further comprising storing the m sums and theircorresponding frequencies.
 13. The method of claim 11 further comprisingadjusting a phase of the data sampling.
 14. The method of claim 11wherein each of the m frequencies corresponds to a frequency code. 15.The method of claim 11 further comprising selecting n and m.
 16. Themethod of claim 11 wherein n is at least
 500. 17. The method of claim 11further comprising initiating the frequency acquisition process inresponse to a change in a data rate.
 18. The method of claim 11 furthercomprising averaging the first peak frequency and the second peakfrequency.